Regarding an optical network, such as a fiber to the home (FTTH), a cable television (CATV), or the like, as disclosed in a patent document 1 as mentioned below, there is used an optical transmission system of passive optical network (PON) type, in which an optical transmission path to be connected with a central office is split by a passive splitter and then constructed for a plurality of customer premises. Such the optical transmission system is called as a passive double star (PDS) as well.
Regarding such the optical transmission system of PON type, as shown in FIG. 19, a splitter 903 is connected with an optical fiber 902 for a user side extended from an optical line termination (OLT) 901 at a central office. Moreover, optical network units (ONU) 905-1 to 905-n (n: natural number; hereinafter, simply referred to as an ONU 905) in a customer premises are connected with a plurality of optical transmission paths split by the splitter 903 to be as optical fibers 904-1 to 904-n (n: natural number; hereinafter, simply referred to as an optical fiber 904).
Moreover, the ONU 905 comprises an optical transceiver unit 910, an ONU function part 920 and a physical layer (PHY)/transform unit 930, and then it is installed indoors to be used. Further, an optical connector 910a is provided at the optical transceiver unit 910 as a connection part at a central office side thereof, and then the optical fiber 904 is connected with the optical connector 910a, which is led into the indoors from outdoor.
While, at a connection side for a peripheral device or the like of the ONU 905, there is provided a local area network (LAN) connector 933 at the PHY/transform unit 930 as an Ethernet (the registered trade name) interface, such as the 10 BASE-TX, the 100 BASE-TX, the 1000 BASE-TX, or the like, and then a LAN cable 934 is connected thereto for example. Moreover, for such the LAN cable 934, a LAN device (an external node) 950, such as a router, a switching hub, or the like, is connected thereto. Or, it may be also available to connect a peripheral device 960, such as a computer or the like, directly to the LAN cable 934. In a case where the LAN device 950 is connected therewith, the peripheral device 960, such as the computer, a printer, or the like, is further connected thereto.
Next, a detailed block diagram of the ONU 905 is shown in FIG. 20. The ONU function part 920 comprises an ONU LSI 921, a flash memory 922 and a synchronous static random access memory (RAM) (the synchronous SRAM) 923. And then the ONU LSI 921 is connected to the optical transceiver unit 910.
Moreover, the PHY/transform unit 930 as the Ethernet (the registered trade name) interface comprises a physical layer (PHY) 931, a transformer 932 and the LAN connector 933. Further, the PHY 931 is connected with a media independent interface (MII) (not shown in figures) of the ONU LSI 921, the transformer 932 is connected with the PHY 931, and then the LAN connector 933 is connected with the transformer 932. Furthermore, as a power supply to be used in the ONU 905 inside, there are provided a power connector 941 and a power supply circuit 942, and then from the power supply circuit 942, a power is supplied to individual component units.
Thus, it is normal for the conventional ONU 905 that has a structure comprising a connection interface to a general LAN cable, an interface for an AC 100V commercial power source, an optical fiber interface and an optical fiber storing part. Here, one example of a general board configuration regarding the conventional ONU 905 is shown in FIG. 21. Moreover, one example of an outside dimension regarding the conventional ONU 905 is shown in FIG. 22. Such the conventional ONU 905 is arranged for all of the above mentioned individual component units thereof on one sheet of a substrate module (board). And then the optical transceiver unit 910 has a structure that an optical transceiver module 910b of a main body thereof and the optical connector 910a are connected therebetween using an optical fiber cord 910c. Hence, according to the conventional ONU, the ONU 905 becomes to be a relatively large equipment with being configured using a single body package as shown in FIG. 22, because all of such the function parts as above mentioned are arranged on the one sheet of the board.
Each example of connecting a LAN device 950 with the conventional ONU 905 is shown in FIG. 23 and FIG. 24. In FIG. 23, there is shown an example that the LAN device 950, such as a compact broad band router or the like, is connected with the ONU 905 via the LAN cable 934. While, in FIG. 24, there is shown an example that a medium size or a small size L2 or L3 LAN switch device, or the LAN device 950, such as the router or the like, is connected with the ONU 905 via the LAN cable 934 as well. Moreover, the optical fiber 904, the LAN cable 934, and a power cable 943 provided with an AC adapter 944 are connected with the ONU 905 for both of the examples.
Moreover, the ONU function part 920 has a function to perform a media access control for the OLT 901 and the external node 950 as being pursuant to the IEEE 802.3ah. Further, as grouping based on a reference model of the open systems interconnection (OSI) instituted by the International Organization for Standardization (ISO), the optical transceiver unit 910 and the PHY/transform unit 930 become to be a physical layer (referred to as an L1 layer hereinafter), and the ONU function part 920 becomes to be a data link layer (referred to as an L2 layer hereinafter). Still further, as redrawing the block diagram of the ONU 905 as shown in FIG. 20 to be a block diagram for every layer according to the reference model of the OSI, it becomes able to be as shown in FIG. 25. Still further, the ONU 905 comprises a component unit of L1 layer and a component unit of L2 layer, and then such the component units are arranged on one sheet of a board, as shown in the similar figure.
Still further, one example that the external node 950 is connected to the ONU 905 via the LAN cable 934 is shown in FIG. 35. FIG. 35 is a diagrammatic perspective view of the ONU 905 and the external node 950. Here, a LED 950a provided at the external node 950 is turned on when a communication is established between the ONU 905 and the external node 950. That is to say, there is provided the LED at the external node, such as a conventional LAN switch or the like, for notifying whether a communication is established for the OLT at the central office via the ONU, and then it is set to be turned on when the communication is established therebetween. Furthermore, there is provided an LED 905a at the ONU 905 of desk top type as shown in FIG. 35, and then it indicates a communication possible state by turning it on when the communication is established for the OLT 901.    [Patent Document 1] Japanese Patent Application Publication No. H09 (1997)-214541